In conventional tool assemblies, a punch shoe may be mounted on the ram of a press and carry one or more punch retainers attached thereto by means of dowels and bolts and carrying one or more punches. Attached to the bed of the press is a die shoe which may have mounted therein a die retainer attached thereto by dowels and bolts and carrying a die button complementary to the punch. Additionally, a stripper plate may be associated with the assembly to strip the stock from the punch as it is withdrawn from the die.
In a typical manufacturing operation for producing a tool assembly as described above, the die sets are first mounted on the die shoe at the desired locations. The punch shoe is then positioned on a suitable supporting surface and the die shoe is positioned over the punch shoe. The punch and die shoes may be provided with interengaging bushings and guide pins for alignment purposes, with the punch shoe having bushing lined openings therethrough and the die shoe having pins mounted at the corners thereof which are slidably received in the bushings in the die shoe.
The necessary number of punch retainers are then positioned on the punch shoe in their approximate positions opposite their respective dies. Each of the punch retainers will include one or more punches projecting therefrom. The punches may be secured in the retainers by means of bolts or the like threaded through the sides of the retainers and engaging detents in the punches to lock the punches in position.
Securing the punches in their retainers in this manner requires moving the punches manually in their sockets while manipulating the bolts until the end of the bolt can be felt entering the detent, then locking the bolt in position. A more convenient manner of assembling the punches in their retainers, and probably a more commonly used method, is to provide the retainers with spring loaded balls which ride in passageways angularly disposed upwardly and outwardly with respect to the punch sockets.
The upward and outward inclination of the passages carrying the spring loaded balls allows the punches to be inserted into the sockets relatively easily but resists forces tending to remove the punches from the sockets, as would be encountered as the punch is withdrawn from stock which it has pierced.
However, after the punch retainers carrying the punches are positioned approximately on the punch shoe, as noted above, it is necessary to bring the die shoe carrying the dies down into close proximity to the punch shoe in order to align the punches with the die openings.
During this operation there is a tendency for the guide pins to bind in the bushings, particularly with very large assemblies in which the shoes may be several feet in length and width. To overcome binding it is common practice to pound or vibrate the shoes. However, this may cause the punch retainers, which are merely resting on the surface of the punch shoe, to jump from the surface of the shoe.
Since the spring loaded balls are intended primarily to resist forces tending to withdraw the punch from the punch socket, when the punch retainers separate from the surface of the punch shoe, the punches may slip further through their sockets and project out the opposite surfaces of the retainers. This results in the punch being cocked with respect to the die with which it is to be aligned and requires removal of the punch and retainer so that the punch may be positioned properly within the punch socket, and this in turn may also necessitate separation of the punch shoes in order to reach the retainer.
Thus, although retainers utilizing spring loaded balls provide advantages over those utilizing bolts to fix the punches in place, their use presents problems during the manufacture of tool assemblies which complicate the manufacturing process and increase its cost.
In further steps in a conventional manufacturing operation, after the retainers carrying the punches have been positioned on the surface of the punch shoe and the die shoe brought into proximity with the underlying punch shoe, it is common practice to align the punches with their opposing dies by visually sighting the punches through the scrap openings in the die shoe and the die openings.
Thereafter, the outline of the retainer is scribed on the surface of the punch shoe and the die shoe is removed from its position overlying the punch shoe. Tool retainers such as the punch retainers are generally purchased by the manufacturer of the punch and die assembly and are provided with precisely located predrilled dowel holes, for a purpose to be described presently, and slightly oversized, predrilled bolt holes.
After the die shoe has been removed from its overlying relationship to the punch shoe, the predrilled retainers are positioned within the scribed lines and, using the predrilled bolt holes as a guide, the location of bolt holes in the punch shoe are marked using a transfer punch. The retainers are then removed and bolt holes drilled and tapped into the punch shoe.
The retainers are then attached to the punch shoe by means of bolts extending through the predrilled bolt holes in the retainers and the bolt holes which have been drilled and tapped in the punch shoe. The bolt holes through the retainers are of somewhat larger diameter than the shanks of the bolts and are counter bored to receive the bolt heads therein.
Therefore, until the bolts are tightened, a limited amount of movement of the retainers on the punch shoes is permitted. The retainers therefore, are attached to the punch shoe without the retainer bolts being tightened and the die shoe is once again brought into position over the punch shoe and, again, sighting through the openings in the die shoe and die, the punches are aligned precisely with the die openings.
Where very precise alignment is required, the punch may have a diameter such that it is received in the die opening without the customary clearance between the inner surface of the die and the outer surface of the punch and the oversize punch is then moved into the die opening to align the punches and dies. Following this, of course, the punch would then be ground down to provide the necessary clearance after it had served its alignment function.
In any case, after the punch has been aligned with the die the retainer bolts are tightened to fix the position of the retainer on the punch shoe. The die shoe is again removed and, using the predrilled dowel holes in the retainer as a guide, matching dowel holes are drilled in the punch shoe.
Usually following this operation, the retainers are unbolted from the punch shoe, a predrilled backing plate of hardened steel interposed between the surface of the punch retainer and the shoe, and the retainer secured to the punch shoe by means of the retainer bolts and press fitted dowels received in the aligned dowel openings.
As noted above, the dowel openings in the retainers are precisely drilled by the retainer manufacturers and, therefore, when, during use of the tool assembly it is necessary to replace the retainers, the new retainers are positioned precisely with their punches in exact alignment with the dies without the necessity of realigning the punches and dies.
The bolts utilized to bolt the retainers to the punch shoes after alignment of the punches and dies are provided with a tool engageable socket in their heads so that they may be tightened by, for example, an Allen type wrench. However, it is often the case that when the die shoe is brought into proximity to the punch shoe so that the punches can be aligned with the dies, there is insufficient clearance between the two shoes to insert a wrench to tighten the retainer bolts.
Therefore, after the punches and dies have been aligned, the die shoe must be raised to allow the retainer bolts to be tightened. Very often this disturbs the alignment of the punches and dies, so that after the retainer bolts are tightened and the die shoe brought down into proximity with the punch shoe to check the alignment, the punches and dies are found to be misaligned.
This necessitates raising the die shoe, loosening the retainer bolts, lowering the die shoe, realigning the punches and dies, raising the die shoe, tightening the retainer bolts, lowering the die shoe to again check the alignment, and, if the punches are again misaligned, repeating the entire process as often as necessary to obtain the alignment of the punches and dies.
While in the above description the dies are described as fixed to the die shoe and the punches aligned with the fixed dies, and also that the die shoe is positioned over the punch shoe during the alignment operations, it will be apparent that in variations of this procedure one or both of these may be reversed.
It has been suggested that a tapped, press fitted nut be inserted in the counter bored holes in the punch retainer and that a drilled and counter bored hole rather than a tapped hole be formed in the punch shoe with the counter bore being at the surface of the shoe opposite the surface thereof adjacent the retainer. However with this construction when the punch shoe is mounted in a press, whenever it is necessary to replace a retainer, the entire shoe must be removed from the press so that access can be had to the bolt head.
It will be apparent, therefore, that in conventional tool assembly manufacturing, the use of conventional tool components often results in excessive amounts of lost time by highly skilled tool makers and, consequently, a substantial increase in manufacturing costs.